



United States Patent Ofi ice 3,125,852 Patented Mar. 24-, 1964 3,125,852MUNQPRUPELLS .lenning P. Blackwell and Richard C. Doss, Bartlesville,

Okla, assignors to Phillips Petroleum Company, a corporation of DelawareNo Drawing. Filed Aug. 12, 1959, Ser. No. 833,353 18 Claims. (Cl.6t)35.4)

This invention relates to monopropellant compositions suitable for usein rocket motors. In a further aspect, this invention relates to amethod of operating such motors.

Rocket motors are operated by burning a mixture of fuel and oxidant in acombustion chamber and causing the resulting gases to be expelledthrough a nozzle at high velocity. Liquid propellants are preferred oversolid propellants where it is necessary to vary thrust during flight.Liquid propellants are classified as bipropellants and monopropellantsand the latter are either a single compound or mixtures of compounds.Monopropellant systems are advantageous in that they require only onetank, one pump, one nozzle, one fuel line, one set of controls, etc.Furthermore, no mixing or proportioning system is required.

The principal elements of a rocket motor utilizing a liquid fuelcomprise a combustion chamber, exhaust nozzle, an injection system, andpropellant control valves. The propellant gases are produced in thecombustion chamber at pressures governed by the chemical characteristicsof the propellant, its rate of consumption, and the cross-sectional areaof the nozzle throat. The gases are ejected into the atmosphere throughthe nozzle with supersonic velocity. The function of the nozzle is toconvert the pressure of the propellant gases into kinetic energy. Thereaction of the discharge of the propellant gases constitute the thrustdeveloped by the rocket motor.

In copending application Serial No. 678,243, filed August 14, 1957, byH. M. Fox, there are disclosed and claimed monopropellant compositionssuitable for use in rocket motors and a method of operating such motorsusing said monopropellants. Broadly speaking, said monopropellantcompositions comprise an amine nitrate and a suitable oxidant, forexample, nitric acid. We have found that the utility of monopropellantscomprising a mixture of an amine nitrate and nitric acid can be enhancedby incorporating a minor amount of a stabilizing agent as definedhereinafter in said mixture. The incorporation of said stabilizing agentincreases the storage stability of said mixtures, i.e., themonopropellant mixture can be stored at higher temperatures for longerperiods of time. Thus, broadly speaking, the present invention comprisesthe use of a stabilized mixture of an amine nitrate and nitric acid as amonopropellant.

An object of this invention is to provide an improved monopropellantcomposition. Another object of this invention is to provide a method ofoperating rocket motors using said improved monopropellant composition.Still another object of this invention is to stabilize a monopropellantcomposition comprising a mixture of an amine nitrate and nitric acid.Other aspects, objects, and advantages of the invention will be apparentto those skilled in the art in view of this disclosure.

Thus, according to the invention there are provided improvedmonopropellant compositions comprising a mixture of (l) a nitric acidoxidant, (2) an amine nitrate,

and (3) a stabilizing agent. Suitable stabilizing agents for use in thepractice of the invention are ammonium nitrate, the alkali metalnitrates, ammonium perchlorate, and the alkali metal perchlorates. Ifdesired, mixtures of said stabilizing agents can be employed.

Further according to the invention there is provided a method ofoperating a rocket motor which comprises the step of injecting themonopropellant compositions of the invention into the combustion chamberof a reaction motor.

Very low concentrations (less than 0.1 weight percent of themonopropellant) of the stabilizing agents of the invention can be usedin the practice of the invention with beneficial results. However, it isusually desirable to use higher concentrations. preferred amount ofstabilizing agent used will be within the range of 0.1 to 10 weightpercent of the monopropellant. However, beneficial efifects result fromthe use of even smaller amounts, e.g. as low as 0.01 percent, andgreater amounts, e.g. 10 to 15 percent, can be used.

Amine nitrates suitable for use in the practice of the inventioninclude, among others, piperidine nitrate, pyridine nitrate, and aminenitrates having a structural formula wherein: each R and each R isselected from the group consisting of acyclic, alicyclic, and aromatichydrocarbon radicals containing from 1 to 8 carbon atoms, and hydrogen,at least one R being one of said hydrocarbon radicals; and R" isselected from the group consisting of and RNR lg! L I JZ radicalswherein R is defined as above, y is an integer of from 1 to 3, z is aninteger of from 1 to 3, and n is an integer of from 1 to 5 the totalnumber of carbon atoms in the molecule does Generally speaking, the 1not exceed 40, and the total number of amino nitrogen atoms in themolecule does not exceed 10.

Examples of amine nitrates suitable for use in the practice of theinvention include, among others, the following:

Methylamine nitrate Dimethylamine nitrate Trimethylamine nitrateEthylamine nitrate Diethylamine nitrate Triethylamine nitratePropylamine nitrate Dipropylamine nitrate Tripropylamine nitrateIsopropylarnine nitrate Tertiary butylamine nitrate Isobutylaminenitrate Cyclopentylamine nitrate Cyclohexylamine nitrate Cyclooctylaminenitrate Dicyclohexylamine nitrate Tricyclohexylamine nitrate4-cyclohexenylamine nitrate Phenylamine nitrate Diphenylamine nitrateTri-n-butylamine nitrate N,N-di-n-octyl-p-tolylamine nitrateo-Methylbenzylamine nitrate N,N,N',N-tetramethylethane-1,2-diaminedinitrate N,N,N,N'-tetraethylethane-1,2-diamine dinitrateN,N,N,N'-tetra-n-octylethane-l,2-diamine dinitrateN,N,N',N'-tetramethylpropane-l,Z-diamine dinitrateN,N,N'N'-tetramethylpropane-1,3-diamine dinitrateN,N,N,N-tetraethylpropane-1,3-diamine dinitrateN,N,N',N-tetrabutylpropane-1,3-diamine dinitrateN,N,N,N'-tetrahexylpropane-1,3-diamine dinitrateN,N,N,N'-tetramethylbutane-1,4-diamine dinitrateN,N,N,N'-tetracyclohexylbutane-1,4-diamine dinitrateN,N,N,N-tetraphenylbutane-1,4-diamine dinitrateN,N,N',N-tetraphenyl-n-4-octene-1,3-diamine dinitrateN,N,N,N'-tetracyclohexylhexane-2,6-diamine dinitrateN,N,N',N'-tetramethyl-2-butenel ,4-diamine dinitrateN,N,N,N--tetramethyl-2-butyne-1,4-diamine dinitrateN,N,N',N'-tetramethyl-2-0ctene-4,S-diamine dinitrateN-phenyl-N-n-octylethane-1,2-diamine dinitrateN,N,N',N-tetra-n-0ctyloctane l,Z-diamine dinitrateN,N-di(2-ethylhexyl)-2-butene-1,4-diamine dinitrateN,N,N,N'-tetraethyl-4-octyne-1,3-diamine dinitrateBis-(N,N-dimethylaminoethyl)ether dinitrate Bis-(N,N-di-n-octylamino-n-butyl) ether dinitrate N-cyclohexylaminopropylN-phenylaminopropyl ether dinitrate N-Z-ethylphenylaminoethylamino-n-butyl ether dinitrate Bis (amino-n-butyl ether dinitrateBis(N,N-di-2-ethylcyclohexylamino-n-butyl)thioether dinitrateBis(aminoethyl)thioether dinitrate Bis(N,N-dimethylaminoethyl)thioetherdinitrate N,N,N,N-tetramethyl-1,3-diamine-2-propanol dinitrateN,N,N,N-tetraethyl-1,9-diamino--nonanol dinitrateN,N,N'-tri-(2-ethylcyclohexyl) -.1,4-diamino-2-butanol dinitrateN,N,N',N',N"-pentamethyldiethylenetriamine trinitrateN,N',N"-tricyclohexyldiethylenetriamine dinitrateN,N,N-tri-n-octyldiethylenetriamine trinitrateN,N,N,N',N",N-hexamethylpropane-1,2,3-triamine trinitrate N ,N ,N ,N ,N,N ,N ,N ,N ,N -decamethylpentanel,2,3,4,5-pentamine pentanitrate N ,N,N ,N ,N -pentaethyltetraethylenepentamine pentanitrateN-ethyl-Z-butynylamine nitrate N-methyl-Z-butynylamine nitrateDi(2-butynyl)amine nitrate N-hexyl-Z-propynylamine nitrateN-propyl-3-hexynylamine nitrate As used herein the term alkali metalnitrates includes sodium nitrate, potassium nitrate, lithium nitrate,rubidium nitrate, and cesium nitrate. The term alkali metal erchloratesincludes sodium perchlorate, potassium perchlorate, lithium perchlorate,rubidium perchlorate and cesium perchlorate.

Since water tends to retard combustion of the acid with the fuel, thenitric acid is preferably substantially free of water. Thus, thepresently most preferred oxidant is anhydrous nitric acid. However,other more dilute nitric acids can be used in the practice of theinvention. White fuming nitric acids and red fuming nitric acids ofvarying concentrations are available commercially, and all are useful inthe practice of this invention. White fuming nitric acid usuallycontains about to 99 weight percent HNO from 0 to 2 weight percent N0and up to about 10 weight percent water. Red fuming nitric acid usuallycontains about 70 to 90 weight percent HNO from 2 to 25 weight percentN0 and up to about 10 weight percent water. Of course, mixtures of theabove described acids can be employed to give an acid having anintermediate composition, and all are useful in the practice of thisinvention. Thus, it has been found that nitric acids of all typescontaining at least about 70 Weight percent HNO are useful as an oxidantin the practice of the invention.

The monopropellants used in the practice of the present invention arepreferably near stoichiometric mixtures of the nitric acid and the aminenitrate. The ratio of fuel component to oxidant can be in the range of0.75 to 1.25 times that of the stoichiometric amount. A slightlyfuel-rich mixture is usually required to give optimum rocket motorperformance.

The monopropellants of the invention can be prepared by adding thestabilizer salt to the fluid mixture compris ing the amine nitrate andthe nitric acid. It is also within the scope of the invention to employany other suitable order of mixing said ingredients, e.g., adding thestabilizer salt to the nitric acid and then adding the amine nitrate tothe resulting mixture. In preparing said monopropellants of theinvention it is preferred that the mixing of said ingredients be carriedout at temperatures below 50 C., e.g., 0 to 30 C.

Amine nitrates can be prepared by several methods. One method is toreact an amine with nitric acid. Another method which can be employed isto form a salt of the amine, such as hydrochloride or an acetate, andthen react the amine salt with nitric acid.

EXAMPLE I A number of runs were made in which polyamine compounds werereacted with nitric acid to form the corresponding amine nitrates. Theseruns were carried out according to the following procedure.

An amount of the pure polyamine compound was charged to a flask, afterwhich an amount of aqueous nitric acid was charged slowly to said flaskby means of a dropping funnel. The temperature of the flask contents wasmaintained within the range of from O to 10 C. by means of an ice bathand by adjusting the rate of addition of the nitric acid to keep thetemperature of the reaction mass below 10 C. During the addition of thenitric acid, the flask contents were stirred vigorously. After thenitric acid had been charged, the flask contents were stirred forseveral minutes to insure complete reaction, after which said fiaskcontents were poured into approximately 5 times its volume of chilledacetone (10 to 25 C.). The amine nitrate precipitated out. Thisprecipitate was recovered by filtration, washed with cold acetone orether, and dried in a vacuum desiccator at room temperature. The meltingpoint and stability of the amine nitrate were then determined. None ofthe amine nitrates which were prepared were found to be shock sensitiveto the blow of a hammer. The results of these runs are given below inTable I.

Table 1 Run No. Amine Charged N, ,N-tetramethylpropane-1,2-diamine.,N-tetramethylbutane-1,3-diamine ,N-tetramethyibutane-1,3-diamine,N-tetramethyl-2-butyne-1,4-diamine ,N N,N'-tetramethylethane-1,2-diamine -dimethylethy1ene-1,2-diamme,N',N-tetramethyl-2-butene-1 4-diamine N ,N-tetraethylpropane-LB-diamine1 In this run, the amine was dissolved in an equal volume of acetone.

EXAMPLE II Monopropellant mixtures were prepared with anhydrous nitricacid obtained by distillation of red fuming nitric acid in the presenceof sulfuric acid. Analyses of typical batches of the distilled acidshowed that the product contained more than 99.8 weight percent HNO andless than 0.2 weight percent oxides of nitrogen.

Said monopropellants were prepared by dissolving an amine salt inseparate portions of freshly prepared acid and then incorporating astabilizing agent of the invention in the solution. The storagestability of the monopropellants thus prepared was measured by thefollowing procedure.

A small glass tube, constructed from fii-inch I.D. glass pipe which willwithstand a pressure greater than 1000 p.s.i.g. is filled abouttwo-thirds full (about 6 ml.) with the monopropellant to be tested. Saidtube is fitted with a safety head containing a blowout disk which willrupture at about 200 p.s.i. pressure. The small glass bomb is thenplaced in a constant temperature bath containing cold Water and isconnected to a pressure recorder and to a supply of compressed nitrogengas. The pressure in said bomb is then increased to about 75 p.s.i.g.with nitrogen to check the system for leaks and, after checking, thepressure in said bomb is reduced to 20 p.s.i.g. The temperature in theconstant temperature bath, which can be regulated to maintain atemperature of 200 F., is increased and the time at which a temperatureof 200 F. is reached is taken as the start of the test. The test isterminated when the pressure in said bomb exceeds 100 p.s.i.g., or whenthe blow-out disk is ruptured (the pressure rise is often rapid after100 p.s.i.g. is reached). The storage life of the monopropellant beingtested is recorded as the time necessary for the pressure in said bombto increase from 20 to 100 ps.i.g. at a temperature of 200 F.

Table II given below shows the weight percent of amine salt and ofstabilizer salt which was mixed with the. anhydrous nitric acid toprepare the monopropellants. is approximately the stoichiometric ratio,i.e. the acid is sufficient to oxidize the amine salt completely tocarbon dioxide, nitrogen, and water.

Comparison of runs 1 and 2 shows that the storage.

stability of the monopropellant is increased from 22.2 to 53 hours byuse of ammonium nitrate. Comparison of run 3 with runs 4 and 5 showsthat the storage stability of the monopropellant was increased from 0.7to 17.25 and from 0.7 to 13.7 hours by use of ammonium perchlorate andammonium nitrate, respectively. These runs illustrate the benefits whichare obtained in the practice of the invention.

The ratio of amine salt to acid in these mixtures.

Percent Yield of Mols Ni- Aqueous Mols Amine M.P. of trio Acid Acid (Wt.Amine Nitrate, Amine N1- Charged Percent Charged Percent trate C HNOa)0.606 40. 5 0. 275 96. 3 220-221 O. 606 33. 4 0.275 92. 3 177-179 0. 60640. 5 0.275 95.0 115-116 1.19 70. O 0. 578 97.0 115-116 0.6 41. 0. 28596. 4 145-146 0. 6 41. 0 0.285 76. 142-143 0. 43 70.0 0.208 98. 7173-174 0. 4O 70. 0 0. 183 94. 3 173-174 0.51 70. 0 1 0.25 72.0 88-93 0.51 70. 0 0. 85. 2 120-124. 0.51 70. 0 0. 25 91. 2 113-114 '0. 70 70. 00. 23 80. 0 162-163 0. 53 70. 0 0. 173 65. 3 104-106 0. 505 60. 0 0. 5not 125 recorded 0. 44 70. 0 0. 21 179-180 0. 42 70. 0 0.2 97. 0 157.5-159. 5

Table II 5 COMPOSITION OF MONOPROPELLANTS AND STORAGE STABILITY AmineWt. Per- Storage Nitrate in cent Stahi- Stability, Run Amine Monopro-Stabilizer lizer in hr. at 200 No. Nitrate pellant, Monopro- F. Wt.Perpellant cent A 29.3 0 0 22. 2 A 27.8 NH NO3 7.1 b 53 13 36 0 0 0. 7 B35. 8 NH4C104. 1 a 1. 7 17. 25 B 35.8 NHiNo3 1.1 13. 7

' Solution was saturated with the salt at room temperature (2025 0.).

EXAMPLE III Ammonium nitrate in the amount of 0.15 gram was dissolved in14.85 grams (9.9 m1.) of essentially anhydrous nitric acid (prepared asdescribed in Example II above). The storage stability at 200 F. of saidsolution was determined in accordance with the procedure described inExample 11 above and was found to be 2.2 hours. A control run made onsaid anhydrous acid containing no ammonium nitrate showed that thestorage stabilityat 200 F. of said acid containing no ammonium nitratewas 28 hours.

Thus ammonium nitrate does not stabilize nitric acid but surprisinglywill stabilize the monopropellants comprising an amine nitrate dissolvedin nitric acid.

-It is to be realized that the storage stability test at 200 F. is avery severe test. The stabilizing agents of the invention are effectivefor increasing the storage stability at temperatures lower than 200 F.Sincethe monopropellants of the invention may possibly be used or storedunder desert conditions, 200 F. has been chosen as a reasonable, yetsevere, maximum temperature at which to measure storage stability.

Various modifications of the invention can be made, or followed, bythose skilled in the art in view of the above disclosure. Suchmodifications are believed to be within the spirit and scope of theinvention.

We claim:

1. A monopropellant composition consisting essentially of a mixture of(1) a nitric acid oxidant containing at least weight percent HNO;.,, (2)an amine nitrate selected from the group consisting of pyridine nitrate,piperidine nitrate, and amine nitrates characterized by a formulaselected from the group consisting of wherein: each R and each R isselected from the group consisting of acyclic, alicyclic, and aromatichydrocarbon radicals containing from 1 to 8 carbon atoms, and hydrogen,at least one R being one of said hydrocarbon radicals; and R" isselected from the group consisting of (a) alkylene, alkenylene, andalkynylene hydrocarbon radicals containing from 2 to 8 carbon atomswherein the carbon atoms attached to the nitrogen atoms are attached toadjoining carbon atoms by single valence bonds, and (b) "'X-]- R"'radicals wherein each R'" is an alkylene radical containing from 2 to 4carbon atoms, and each X is selected from the group consisting ofoxygen, sulfur, and

radicals wherein R is defined as above, y is an integer of from 1 to 3,z is an integer of from 1 to 3; and n is an integer of from 1 to 5; thetotal number of carbon atoms in the molecule does not exceed 40, and thetotal number of amino nitrogen atoms in the molecule does not exceed 10,and (3) a stabilizing agent selected from the group consisting ofammonium nitrate, the alkali metal nitrates, ammonium per chlorate, thealkali metal perchlorates, and mixtures thereof; the ratio of said aminenitrate to said nitric acid oxidant in said mixture being withn therange of 0.75 to 1.25 times that of the stoichiometric amount, and saidstabilizing agent being present in an amount within the range of 0.01 to15 weight percent of said mixture.

2. The composition of claim 1 wherein said stabilizing agent is presentin an amount within the range of 0.1 to weight percent of said nitricacid oxidant.

3. The composition of claim 1 wherein said stabilizing agent is ammoniumnitrate.

4. The composition of claim 1 wherein said stabilizing agent is sodiumnitrate.

5. The composition of claim 1 wherein said stabilizing agent ispotassium nitrate.

6. The composition of claim 3 wherein said amine nitrate isN,N,N',N'-tetraethylpropane-1,3-diamine dinitrate.

7. The composition of claim 3 wherein said amine nitrate isN,N,N',N'-tetramethylpropane-1,3-diamine dinitrate.

8. The composition of claim 1 wherein said stabilizing agent is ammoniumperchlorate.

9. The composition of claim 1 wherein said stabilizing agent is sodiumperchlorate.

10. The composition of claim 1 wherein said stabilizing agent ispotassium perchlorate.

11. The composition of claim 8 wherein said amine nitrate isN,N,N,N'-tetraethylpropane-1,3-diamine dinitrate.

12. The composition of claim 8 wherein said amine ni- 8 trate isN,N,N',N-tetramethylpropane-1,3-diamine dinitrate.

13. In the method for development of thrust by the combustion of amonopropellant in the combustion chamber of a reaction motor, the stepcomprising injecting into said combustion chamber a mixture of (1) anitric acid oxidant containing at least 70 weight percent HNO;,, (2) anamine nitrate selected from the group consisting of pyridine nitrate,piperidine nitrate, and amine nitrates characterized by a formulaselected from the group consisting of wherein: each R and each R isselected from the group consisting of acyclic, alicyclic, and aromatichydrocarbon radicals containing from 1 to 8 carbon atoms, and hydrogen,at least one R being one of said hydrocarbon radicals; and R" isselected from the group consisting of (a) alkylene, alkenylene, andalkynylene hydrocarbon radicals containing from 2 to 8 carbon atomswherein the carbon atoms attached to the nitrogen atoms are attached toadjoining carbon atoms by single valence bonds, and (b) {-R"X-} R"'-radicals wherein each R is an alkylene radical containing from 2 to 4carbon atoms, and each X is selected from the group consisting ofoxygen, sulfur, and

radicals wherein R is defined as above, y is an integer of from 1 to 3,z is an integer of from 1 to 3, and n is an integer of from 1 to 5; thetotal number of carbon atoms in the molecule does not exceed 40, and thetotal number of amino nitrogen atoms in the molecule does not exceed 10,and (3) a stabilizing agent selected from the group consisting ofammonium nitrate, the alkali metal nitrates, ammonium perchlorate, thealkali metal perchlorates, and mixtures thereof; the ratio of said aminenitrate to said nitric acid oxidant in said mixture being within therange of 0.75 to 1.25 times that of the stoichiometric amounts, and saidstabilizing agent being present in an amount within the range of 0.01 to15 weight percent of said mixture.

14. The method of claim 13 wherein said stabilizing agent is ammoniumnitrate.

15. The method of claim 13 wherein said stabilizing agent is ammoniumperchlorate.

16. The method of claim 14 wherein said amine nitrate isN,N,N',N'-tetraethylpropane-1,3-diamine dinitrate. 17. The method ofclaim 15 wherein said amine nitrate isN,N,N',N'-tetramethylpropane-1,3-diamine dinitrate.

18. The method of claim 13 wherein said stabilizing agent is present inan amount within the range of 0.1 to 10 percent by weight of saidmixture.

References Cited in the file of this patent UNITED STATES PATENTS2,951,335 Stengel Sept. 6, 1960

13. IN THE METHOD FOR DEVELOPMENTG OF THRUST BY THE COMBUSTION OF AMONOPROPELLANT IN THE COMBUSTION CHAMBER, OF A REACTION MOTOR, THE STEPCOMPRISING INJECTING INTO SAID COMBUSTION CHAMBER A MIXTURE OF (1) ANITRIC ACID OXIDANT CONTAINING AT LEAST 70 WEIGHT PERCENT HNO3, (2) ANAMINE NITRATE SELECTED FROM THE GROUP CONSISTING OF PYRIDINE NITRATE,PIPERIDINE NITRATE, AND AMINE NITRATES CHARACTERIZED BY A FORMULASELECTED FROM THE GROUP CONSISTING OF